IV-491 



In general, estuarine system diversity and organization is highest 

 where energy inputs are high and stresses are low as in many 

 relatively unmodified temperate and tropical estuarine areas. 

 Conversely, those systems where stresses are high and sources of 

 energy low are characterized by low species diversity and 

 relatively simple organization as in the case of artic systems or 

 those greatly modified by man. Thus, the relative diversity and 

 organization of estuarine systems are due to both "natural" 

 occurrences, such as sunlight, temperature fluxes and nutrient 

 inflows, as well as those associated with man's activities such as 

 modification of circulation regimes, addition of pollutants to the 

 water, and thermal waste heating. 



Estuarine systems in the United States are almost universally 

 stressed by both natural and man-induced processes. The relative 

 mixture of man-caused and naturally occurring stresses, and their 

 respective roles in estuarine modification, are presently little 

 known, and difficult to separate. It is certain, however, that the 

 stresses resulting from man's present and potential activities in 

 the estuarine zone play a decisive and increasing role in the 

 foreseeable future operation of estuarine ecologies. Therefore, 

 the following discussion focuses upon man's activities as they 

 relate to modification of existing estuarine systems. 



